The goal of these experiments is a better understanding of pulsatile blood flow in the mammalian circulation. Specifically, we seek to identify and describe systematically: (1) the factors that determine the pulsatile characteristics of pressure and flow waves; (2) the transformation of these waves as they travel through the major vessels and regional vascular beds; (3) the changes that occur in vascular impedance and wave propagation under various physiologic conditions; (4) the neurohumoral mechanisms that control and regulate these changes. Vascular impedance and propagation coefficients will be measured in large arteries in vivo, in vascular beds in situ, and in isolated vessel segments, using the dog as the experimental animal in most cases. The viscoelastic properties of blood vessels will also be determined by direct measurements of instantaneous vascular diameters and distending pressures. The clinical and physiologic significance of the information sought lies in the fact that vascular elasticity determines in part the work demanded of the heart, and also in the possibility that function of some organ systems is influenced by the amount of pulsation transmitted to the microcirculation. BIBLIOGRAPHIC REFERENCES: Milnor, W. R. and Nichols, W. W.: A New Method of Measuring Propagation Coefficients and Characteristic Impedance in Blood Vessels. Circulation Research 36: 631-639, 1975. Milnor, W. R.: Arterial Impedance as Ventricular Afterload. Circulation Research 36: 565-570, 1975.